The present invention relates generally to an improved composite material. More specifically, the present invention relates to a thermally conductive composite material that is easily moldable or castable.
In the heat sink industries, it has been well known to employ solid metallic materials for thermal conductivity applications, such as heat dissipation for cooling semiconductor device packages. For these applications, such as heat sinks, the metallic material typically is tooled or machined from bulk metals into the desired configuration. However, such metallic conductive articles are typically very heavy, costly to machine and are susceptible to corrosion. Further, the geometries of machined metallic heat dissipating articles are very limited to the inherent limitations associated with the machining or tooling process. As a result, the requirement of use of metallic materials which are machined into the desired form, place severe limitations on heat sink design particular when it is known that certain geometries, simply by virtue of their design, would realize better efficiency but are not attainable due to the limitations in machining metallic articles.
It is widely known in the prior art that improving the overall geometry of a heat-dissipating article can greatly enhance the overall performance of the article even if the base material used in the heat sink is the same. Therefore, the need for improved heat sink geometries necessitated an alternative to the machining of bulk metallic materials. To meet this need, attempts have been made in the prior art to provide molded compositions that include conductive filler material therein to provide the necessary thermal conductivity. The ability to mold a conductive composite enabled the design of more complex part geometries to realize improved performance of the part.
The attempts in the prior art included the employment of a polymer base matrix loaded with a granular material, such as boron nitride grains. Also, attempts have been made to provide a polymer base matrix loaded with flake-like filler material. In addition, attempts have been made using Metal Injection Molding Material (MIM). These attempts are, indeed, formable into complex geometries but still do not approach the desired performance levels found in metallic machined parts and the MIM parts have a lower thermal conductivity than heat sinks machined from solid metal. In addition, known conductive plastic materials are undesirable because they are typically very expensive to manufacture because they employ very expensive filler materials. Still further, these conductive composite materials must be molded with extreme precision due to concerns of filler alignment during the molding process. Even with precision molding and design, inherent problems of fluid turbulence, collisions with the mold due to complex product geometries make it impossible to position the filler ideally thus causing the composition to perform far less than desirable.
Moreover, the entire matrix of the composition must be satisfactory because heat transfer is a bulk property rather than a direct path property such as the transfer of electricity. A direct path is needed to conduct electricity. However, heat is transferred in bulk where the entire volume of the body is employed for the transfer. Therefore, even if a highly conductive narrow conduit is provided through a much lower conductive body, the heat transfer would not be as good as a body which is consistently marginally conductive throughout the entire body. Therefore, consistency of the thermal conductivity of the entire matrix of the composite body is essential for overall high thermal conductivity.
In view of the foregoing, there is a demand for a composite material that is highly thermally conductive. In addition, there is a demand for a composite material that can be molded or cast into complex product geometries. There is also a demand for such a moldable article that exhibits thermal conductivity as close as possible to purely metallic conductive materials while being relatively low in cost to manufacture.